Nepalese passport holders do NOT require any kind of Visa while travelling thru Delhi. Most KTM bound flights from the US have an overnight layover in Delhi's Indira Gandhi International (IGI) airport, where you have to check out their luggage after they arrive at night and check in again the next day while boarding the flight to KTM. You can even go out of the airport and stay in a hotel/motel in Delhi. But BE sure to have a prepaid taxi from the airport authorities and get hotel info before u board the taxi

No clue abt Amsterdam but believe you do NOT require a transit visa as its one of the most busy imternational hubs in Europe. But be sure to check on this.